The present disclosure relates to an antenna circuit, a communication device, and a communication method, and in particular, relates to an antenna circuit, a communication device, and a communication method which are able to improve degradation of communication performance.
A reader/writer in the related art outputs a carrier signal to a non-contact IC card, or a mobile phone when receiving a signal from the non-contact IC card, or the mobile phone. When the non-contact IC card, or the mobile phone performs a load modulation with respect to the carrier signal, an amount of change thereof is extracted from a portion of an antenna circuit which adjusts an impedance, and is input to a reception terminal of a reception circuit of the reader/writer. In this manner, a reception of a signal from the non-contact IC card, or the mobile phone has been performed (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-235884).
Meanwhile, the quality of a signal which is input to a reception circuit is changed depending on a positional relationship between the non-contact IC card, or the mobile phone and an antenna of the reader/writer. The signal quality is determined by a result of an impedance adjustment, and differs depending on a type of card, or the like. The reception circuit of the reader/writer performs decoding based on the signal. However, there has been a case where the decoding is difficult depending on the signal quality, and as a result, a communication distance of the reader/writer shortens, or a communication performance worsens in a certain positional relationship.
On the other hand, it is also possible to perform an antenna adjustment so that the quality of a reception signal becomes good, however, when performing the antenna adjustment, it is difficult to output a magnetic field efficiently from the reader/writer, and as a result, there is a concern that the communication distance may shorten.